A novel combination of living polymerization reactions has been proposed for the controlled synthesis of poly(alkyl methacrylate)-graft-polylactones. This strategy relies upon the sequential living ... [more ▼]

A novel combination of living polymerization reactions has been proposed for the controlled synthesis of poly(alkyl methacrylate)-graft-polylactones. This strategy relies upon the sequential living polymerization of alkyl methacrylates and aliphatic lactones, with an intermediate chemical transformation for shifting from the first mechanism to the second one. In the first step, an alkyl methacrylate (methyl and butyl) is copolymerized with 2-trimethylsiloxyethyl methacrylate (TMSEMA). This living anionic polymerization is initiated with diphenylhexyllithium( DPHLi) in the presence of a μ-ligand, lithium chloride, in THF at - 78 °C. The trimethylsiloxy groups are then hydrolyzed with release of hydroxyl groups which are reacted with triethylaluminum in order to form a multifunctional macroinitiator of the Al alkoxide type. The second step consists of the ring opening polymerization (ROP) of aliphatic lactones (ε-caprolactone, J-valerolactone and 1,4,8-trioxaspiro[4.6]-9-undecanone (TOSUO)) with the formation of novel graft copolymers. As a result of the livingness of both the anionic and the ROP polymerization steps, the molecular weight of both the main backbone and the grafts is predictable, the apparent polydispersity is narrow ( from 1.05 to 1.30) and the grafting density can be controlled being dependent on the distribution of the hydroxyl groups within the precursor backbone. [less ▲]

Copolymerization of binary mixtures of alkyl (meth)acrylates has been initiated in toluene by a mixed complex of lithium silanolate (s-BuMe2SiOLi) and s-BuLi (molar ratio > 21) formed in situ by reaction ... [more ▼]

Copolymerization of binary mixtures of alkyl (meth)acrylates has been initiated in toluene by a mixed complex of lithium silanolate (s-BuMe2SiOLi) and s-BuLi (molar ratio > 21) formed in situ by reaction of s-BuLi with hexamethylcyclotrisiloxane (D3). Fully acrylate and methacrylate copolymers, i.e., poly(methyl acrylate-co-n-butyl acrylate), poly(methyl methacrylate-co-ethyl methacrylate), poly(methyl methacrylate-co-n-butyl methacrylate), poly(methyl methacrylate-co-n-butyl methacrylate), poly(isobornyl methacrylate-co-n-butyl methacrylate), poly(isobornyl methacrylate-co-n-butyl methacrylate) of a rather narrow molecular weight distribution have been synthesized. However, copolymerization of alkyl acrylate and methyl methacrylate pairs has completely failed, leading to the selective formation of homopoly(acrylate). As result of the isotactic stereoregulation of the alkyl methacrylate polymerization by the s-BuLi/s-BuMe2SiOLi initiator, highly isotactic random and block copolymers of (alkyl) methacrylates have been prepared and their thermal behavior analyzed. The structure of isotactic poly(ethyl methacrylate-co-methyl methacrylate) copolymers has been analyzed in more detail by Nuclear Magnetic Resonance (NMR). [less ▲]

The end-capping with 1,1-diphenylethylene (DPE) of living 1,4-poly(diene) lithiated anions prepared in cyclohexane (Chx) and toluene is a major but poorly controlled step in the synthesis of syndiotactic ... [more ▼]

The end-capping with 1,1-diphenylethylene (DPE) of living 1,4-poly(diene) lithiated anions prepared in cyclohexane (Chx) and toluene is a major but poorly controlled step in the synthesis of syndiotactic poly(methyl methacrylate) (sPMMA) containing block copolymers. The kinetics of the reaction have been studied by means of 7Li NMR not only in Chx and toluene but also in their mixtures with polar solvents, since the solvent polarity must be increased for MMA to be predominantly converted into sPMMA. Although the addition of a polar solvent (tetrahydrofuran (THF), diethyl ether) to Chx and toluene is known to increase the reactivity of living polymeric anions, contaminating lithium salts, such as lithium hydroxide, slow down the end-capping reaction even when 10 vol.-% polar solvent is added. Moreover, the polymeric diphenylalkyllithium anions are unstable in 1/9 (v/v) THF/Chx mixture, as a result of the nucleophilic attack of THF. On the basis of all these observations, new experimental conditions are proposed for improving the control of the anionic block copolymerization of 1,3-dienes and MMA to yield 1,4-poly(diene) and sPMMA containing block copolymers. [less ▲]

Recent developments in the macromolecular engineering of aliphatic polyesters have been overviewed. First, aluminum alkoxides mediated living ring opening polymerization (ROP) of cyclic (di)esters, i.e., lactones, lactides, glycolide, is introduced. An insight into this so-called "coordination-insertion" mechanism and the ability of this living polymerization process to prepare well-defined homopolymers, telechelic polymers, random and block copolymers is then discussed. In the second part, the combination of the living ROP of (di)lac-tones with other well-controlled polymerization mechanisms such as anionic, cationic, free radical, and metathesis polyadditions of unsaturated comonomers, as well as polyconden-sations, is reported with special emphasis on the design of new and well-tailored macromolecular architectures. As a result of the above synthetic breakthrough, a variety of novel materials have been developed with versatile applications in very different fields such as biomedical and microelectronics. [less ▲]

A new type of macromolecular architecture, denoted as dendrimer-like star block copolymers, is reported. These block copolymers are described by a radial geometry where the different generations or layers ... [more ▼]

A new type of macromolecular architecture, denoted as dendrimer-like star block copolymers, is reported. These block copolymers are described by a radial geometry where the different generations or layers are comprised of high molecular weight polymer emanating from a central core. A hexahydroxyl functional core was used as an initiator for the “living” ring opening polymerization (ROP) of ε-caprolactone producing a hydroxyl terminated six arm star polymer with controlled molecular weight and narrow polydispersities (PD < 1.1). Capping these chain ends with dendrons containing activated bromide moieties produced “macro-initiators” for atom transfer radical polymerization (ATRP). Methyl methacrylate was polymerized from these “macro-initiators” in the presence of an organometallic promoter to produce the requisite dendrimer-like star polymers. High molecular weight was obtained with low polydispersities (<1.2). Alternatively, amphiphilic character could be introduced by designing the different layers or generations to be either hydrophobic or hydrophilic. For example, methyl methacrylate (MMA) with either hydroxyethyl methacrylate (HEMA) or methacrylate functional ethylene oxide macromonomers (EO) were polymerized from these “macro-initiators” to provide a hydrophilic outer layer. The use of macromolecular building blocks allows rapid attainment of high polymer in a limited number of steps with purification between transformation requiring only polymer precipitation. [less ▲]

in European Journal of Inorganic Chemistry (1998), 1998(11), 1711-1720

The possibility of grafting a series of alkyl polyacrylates and polymethacrylates onto a nickel cathode by electropoly-merization of the parent monomers has been investigated and has emphasized the ... [more ▼]

The possibility of grafting a series of alkyl polyacrylates and polymethacrylates onto a nickel cathode by electropoly-merization of the parent monomers has been investigated and has emphasized the critical importance of the solvent used. Indeed, the intensity of the inhibition peak, which is the electrochemical mark of the cathode passivation as result of the polymer grafting, clearly depends on both the polarity and the donor-acceptor properties of the solvent. The Gutmann concept is used to account for these experimental results. An increase in the donicity of the solvent used for the electrochemical medium has allowed, for the very first time, several polyacrylates and polymethacrylates [such as poly(ethyl acrylate), poly(methyl methacrylate), and poly(2-trimethylsilyloxyethyl methacrylate)] to be electrografted onto Ni. This observation is consistent with a competition process between the monomer and the solvent for being adsorbed on the cathode and amassing in its very close vicinity. The outcome of this competition is controlled by the relative polarity (in case of low donicity) and the relative donor-acceptor properties (when the difference is high enough) of the monomer/solvent pair, and by the monomer concentration (in case of weak competition). A semiquantitative relationship has also been observed between the monomer ability to be electrografted and the electron-accepting character of the vinyl β-carbon atom as measured by 13C NMR. [less ▲]

Polybutadiene samples of different molecular weight have been synthesized by anionic polymerization as initiated by sec-butyllithium with low polydispersity and a major content of 1,2-vinyl units. They ... [more ▼]

Polybutadiene samples of different molecular weight have been synthesized by anionic polymerization as initiated by sec-butyllithium with low polydispersity and a major content of 1,2-vinyl units. They have been analyzed by time-of-flight secondary ion mass spectrometry (ToF-SIMS) in order to investigate the sensitivity of this method toward the sec-butyl end group and toward the molecular weight. The SIMS spectra show the characteristic fragment of the end group, C4H9+ at m/z = 57, whose the peak intensity is strongly dependent on the polymer molecular weight, as is the case for almost all the fragment intensities. A model consistent with the peak intensity variations is used to give some new insights into the fragmentation mechanism at the end groups and within the main chain. Moreover, the analysis of the end group fragment allows Mn to be readily determined up to Mn = 4 × 104 from, for example, the Y(53)/Y(57) intensity ratio where Y(53) is the intensity of the deprotonated repeat unit ([M − H]+). Other Mn calibration methods have also been used and are discussed in terms of their accuracy and physical meaning. [less ▲]

Combination of the living ring-opening polymerization (ROP) of ε-CL and lactides with the "controlled" free radical polymerization of styrene and methacrylic monomers is a versatile strategy for the ... [more ▼]

Combination of the living ring-opening polymerization (ROP) of ε-CL and lactides with the "controlled" free radical polymerization of styrene and methacrylic monomers is a versatile strategy for the synthesis of well-defined block and graft copolymers. In this respect, the dual "living" polymerization strategy in which two different functional groups on a single molecule used to initiate the two controlled mechanisms is particularly efficient. Combination of ROP and step-growth polymerization is another versatile methodology for the preparation of a large variety of new materials, e.g. polyimide nanofbams, polyester/silica hybrid materials and star and branched polyesters by dendritic initiation. [less ▲]

As an illustration of the frantic development of (meth)acrylic esters anionic polymerization during the last decade, three significant breakthroughs will be presented and analyzed: - extension of the LAP ... [more ▼]

As an illustration of the frantic development of (meth)acrylic esters anionic polymerization during the last decade, three significant breakthroughs will be presented and analyzed: - extension of the LAP (ligated anionic polymerization) concept to the practical synthesis of both high iso- or syndio high MW PMMA; - the production of "perfect" hydrocarbon gels from tailored PMMA-polybutadiene-PMMA triblock copolymers; - the use of reactivity "boosters" allowing to climb back up the nucleophilic reactivity scale, i.e. initiating styrene, dienes and (meth)acrylates polymerization with alcoholates and silanolates. [less ▲]

Just one step is required for the synthesis of block copolymers by simultaneous living/controlled ring-opening and radical polymerization initiated by a difunctional (A-B) compound (shown schematically on ... [more ▼]

Just one step is required for the synthesis of block copolymers by simultaneous living/controlled ring-opening and radical polymerization initiated by a difunctional (A-B) compound (shown schematically on the right). [less ▲]

Interactions of lithium 2-(2-methoxyethoxy)ethoxide (LiOEEM) with the model dimer di-tert-butyl 2-lithio-2,4,4-trimethylglutarate (A) and the living poly(tert-butyl methacrylate) oligomers (B) were ... [more ▼]

Interactions of lithium 2-(2-methoxyethoxy)ethoxide (LiOEEM) with the model dimer di-tert-butyl 2-lithio-2,4,4-trimethylglutarate (A) and the living poly(tert-butyl methacrylate) oligomers (B) were studied in tetrahydrofuran-d8 at 203−273 K using 1H, 13C, 7Li, and 6Li, 1D and 2D, NMR and ab initio SCF 3-21G and MNDO quantum chemical calculations. LiOEEM is shown to have a strong tendency to self-aggregation, producing dimeric, trimeric, and tetrameric aggregates and competing with its mixed aggregation (or complexation) with A and, in particular, B. When dissolved in THF, LiOEEM as well as its mixtures with A form metastable systems which relax in several days at 258 K into equilibrium. Interaction of LiOEEM with A leads to a system of mixed aggregates LiOEEM1A1, LiOEEM3A1, and possibly LiOEEM2A1 along with the original components, in relative populations depending on the LiOEEM/A molar ratio, temperature, time, and probably other factors of preparation. Probable structures of these complexes are proposed, and the nature of the prevalent bonding is suggested. Experimental results indicate that LiOEEM is unable to convert A completely at moderate excess (up to 4/1 mol/mol). Interaction of LiOEEM with B leads to quite analogous complexes but with even lower yields. There appear to be traces of uncomplexed B even at the LiOEEM/B ratio of 10 mol/mol. This is suggested to produce at least two different kinds of active growth centers in the corresponding ligated anionic polymerization of tert-butyl methacrylate and, consequently, the observed bimodality of the polymeric product. The difference with respect to methyl methacrylate, where LiOEEM ensures an almost ideal living polymerization, is suggested to be due to the steric hindrance of efficient complexation exerted by the tert-butyl group. [less ▲]

Interactions of living oligomers of tert-butyl methacrylate (tBuMA) with a Li counterion and of the model living dimer di-tert-butyl 2-lithio-2,4,4-trimethylglutarate (A) with LiCl (B) were studied in ... [more ▼]

Interactions of living oligomers of tert-butyl methacrylate (tBuMA) with a Li counterion and of the model living dimer di-tert-butyl 2-lithio-2,4,4-trimethylglutarate (A) with LiCl (B) were studied in tetrahydrofuran-d8 (THF-d8) solution by 7Li, 6Li, 1H, and 13C, 1D and 2D, NMR spectroscopy. Di-tert-butyl 2-lithio-2,4,4-trimethylglutarate is shown to form a 1:1 complex with lithium chloride in THF. 1H, 7Li NMR results suggest that a rapid equilibrium between free LiCl and the mixed complex takes place when the molar ratio LiCl:lithiated dimer is higher than 1. From 13C relaxation times, a dimeric aggregation (i.e. A2B2) of the complex is deduced, in full accord with MNDO calculations. Preliminary results are presented for living tBuMA oligomers prepared by initiation with diphenylhexyllithium in the presence of various amounts of lithium chloride. Fast-acquired 13C NMR spectra of the living ends were recorded using 13C-enriched monomer added at the end of the polymerization. Their structure is shown to be affected by the amount of LiCl added and to correspond to an equilibrium between free lithium chloride and a complexed end group. A higher excess of LiCl apparently does not change the nature of the complexed living end. The oligomers exhibit marked self-termination in THF at 273 K. Finally, a correlation of the structure of the living chain ends with the macromolecular parameters of the resulting polymer is attempted. [less ▲]

Highly branched poly(ε-caprolactones) with novel and well-defined molecular architectures have been synthesized by the use of new multifunctional initiators. The ring-opening polymerization methods used ... [more ▼]

Highly branched poly(ε-caprolactones) with novel and well-defined molecular architectures have been synthesized by the use of new multifunctional initiators. The ring-opening polymerization methods used to prepare these new structures allowed accurate control of molecular weight and narrow molecular weight distributions. In addition, the synthesis of even more complex molecular architectures was possible by the use of 1,4,9-trioxaspiro[4.6]-9-undecanone as a comonomer with ε-caprolactone. After copolymerization, complete deacetalization of the polyester chains into the corresponding ketone groups followed by quantitative reduction formed polymers with hydroxyl pendant groups. With this synthetic strategy, significant additional functionality was introduced. In addition, the pendant hydroxyl groups along the chains can serve as macroinitiators for the further initiation of ε-caprolactone to prepare dendri-graft molecular architectures. The new polymers were characterized by 1H NMR, 13C NMR, and size exclusion chromatography (SEC). 13C NMR spectra clearly showed that the hydroxyl groups of the initiators were fully substituted to give polymers with two, four, and six arms. [less ▲]

This paper presents the results of slurry polymerisation of ethylene that has been initiated by an Al/Ti/Mg-alcohol supported catalyst. Special attention has been paid to the effects of hydrogen, catalyst ... [more ▼]

This paper presents the results of slurry polymerisation of ethylene that has been initiated by an Al/Ti/Mg-alcohol supported catalyst. Special attention has been paid to the effects of hydrogen, catalyst composition and addition of an α-olefin on catalyst efficiency, molecular weight, crystallinity, and physico-mechanical properties of the final polyolefin. The efficiency of this Al/Ti/Mg catalyst, molecular weight and melting temperature of the formed High Density Polyethylene (HDPE) has been found to decrease as the partial pressure of hydrogen is increased. In parallel, crystallinity and elongation at break of HDPE increase. The composition of this Al/Ti/Mg catalyst has a marked effect on catalyst efficiency, e.g. decrease in the Ti relative content results in an improved efficiency from 86 to 7942 kg PE g-l Ti h-1 as the Mg/Ti molar ratio is increased from 1 to 333. Copolymerisation with 1-octene has also been investigated. When ethylene polymerisation is carried out with this Al/Ti/Mg catalyst at a Mg/Ti ratio of 333, addition of the cr-olefin is responsible for a decrease in the polymerisation rate, which is typical of a negative 'comonomer' effect. This effect is still more pronounced in the presence of H2. Comparison with other catalytic systems has been made in order to understand the role played by the cr-olefin and/or hydrogen on the catalyst efficiency and the physico-mechanical properties of the resulting polyolefins. [less ▲]

The ring-opening polymerization of 1,4,8-trioxaspiro-[4,6]-9-undecanone (TOSUO) initiated by aluminum isopropoxide, Al(OiPr)3, is typically "living" and allows random and block copolyesters of predictable molecular weight and composition to be prepared. Deacetalization of the polyester chains is complete, and reduction of the accordingly formed ketone groups into hydroxyl groups as well. No chain scission is observed when these two derivatization reactions are carried out. The potential of these novel functional aliphatic polyesters has been discussed as drug colloidal vectors and macroinitiators for the synthesis of biodegradable and biocompatible comb, graft and even hyperbranched polymers. [less ▲]

Dynamic mechanical properties, structure and morphology of tetraethoxysilane/poly(ε-caprolactone) (TEOS/ PCL) hybrid materials have been analysed by dynamic mechanical spectroscopy, small-angle X-ray scattering, transmission electron microscopy, and image analysis. The experimental observations agree with a microscopic phase separation of the two constitutive components: the organic polymer and the silica network. The effect of the PCL functional end-groups, the number of functional end-groups per PCL chain, the PCL molecular weight and content, and the curing conditions have been studied on the structure and properties of the hybrid materials. Finally, phase morphology has proved to be co-continuous, at least when the weight composition is close to 50% for each component (SiO2 and PCL), with a characteristic length between the PCL and silica phases of ca. 5 nm, as estimated by image analysis of transmission electron micrographs. [less ▲]